New federal regulations have established standards for the integrity, or worthiness of the airtight seals included in the evaporative fuel systems of motor vehicles. In response, many state regulatory agencies are requiring periodic testing of the evaporative fuel systems of vehicles so equipped. Such testing is typically done at centralized stations employing a plurality of inspection and testing lanes. The "through-put", or average time required to complete the required inspection and testing at such facilities is always under review for improvement. However, certain testing procedures have heretofore required a certain amount of physical disassembly and reassembly of vehicle components to complete testing.
For example, a current method for testing evaporative systems requires that the fuel vapor vent hose, leading from the fuel tank to the system's charcoal canister, be disconnected at the canister. Then, the hose is connected to a testing device which pressurizes the fuel tank and the remainder of the system for a predetermined period, during which pressure is monitored to detect possible leaks in the system's seals. After the test is complete, the hose must again be restored to its original connection to the canister. Such a testing method is classified as "intrusive" in the industry, and exhibits a number of significant disadvantages.
It is estimated that in approximately ten to twenty percent of the vehicles, the charcoal canisters of the evaporative systems are simply inaccessible. Such vehicles would require a waiver from testing, resulting in a significant number of vehicles never being tested for harmful or unsafe fuel vapor leaks. Also, the process of locating, disconnecting, testing, and reconnecting the correct canister hose is time consuming, increasing through-put time for the testing facilities. Finally, there is a risk of damaging some of the components which must be detached, moved, and reattached to complete the testing. Component damage is particularly likely for older vehicles and for vehicles which have an awkward canister location.
The intrusive method does have one advantage, however, in that it tests the seal integrity of all of the evaporative system components of interest, as a functioning, integrated system. These components typically include the vapor vent hose interconnecting the charcoal canister and the fuel tank, the fuel tank, the fuel filler neck, and the fuel tank filler cap. Representative U.S. Patents showing these components as a system, together with a dedicated testing or fault detection device for certain aspects of the fuel system, include U.S. Pat. Nos. 4,962,744, issued to Uranishi et al., and 5,143,035, granted to Kayanuma.
The prior art also includes non-intrusive testing devices, designed to eliminate most of the above-identified problems associated with the intrusive approach. Thus far, such non-intrusive testing systems contemplate the removal of the fuel tank filler cap and the connection of a pressurization and metering device to the filler neck opening. For example, U.S. Pat. No. 5,239,858, issued to Rogers et al., shows the connection of a helium cylinder and a flow meter to an evaporative system, using a connector cap on the filler neck. Such a testing apparatus still requires that the fuel tank filler cap be tested separately for sealing abilities on a "dummy" filler neck, connected to additional testing apparatus.
Separate testing of the filler cap is the prime disadvantage of this non-intrusive technique, as it does not test the sealing capability of the vehicle's actual filler cap against its own filler neck. In other words, it does not test these components as an operating system, and thus may produce inaccurate, unpredictable results. And, since the filler cap and filler neck components are those which are subject to the greatest wear in an evaporative system, the inability of this prior art apparatus to test these components as a system is a serious deficiency.